First of all, to avoid misunderstandings, for the present application following prescribed terminology shall be used in connection with technical terms of a vehicle wheel. With reference to FIG. 1, the whole object shall be understood as wheel 100, which can be made of an applicable material alike an aluminum alloy. The part of the wheel 100 on which a tire (not shown) is to be mounted shall be understood as the rim 110 and the edges of the rim 110 preventing a tire from getting off the rim 110 is known as the bead 115 of the rim. The middle of the wheel 100, where it normally is mounted to a vehicle is called the hub 105 of the wheel 100, the elements connecting the hub 105 and the rim 110 are so-called spokes 120. The area where the spokes 120 merge the rim 110 is herein considered as the base 125 of a spoke 120. In this context a vehicle may be a motor driven vehicle, a motorcycle, a car, a truck, or even an airplane the landing gear of which also comprises wheels. In other words, any kind of object with turning wheels, the wheels of which may be subject to the method or apparatus of the present application.
Wheels for vehicles require balancing to counter unbalances. So-called Hidden Spokes Placement (HSP) requires the balancing weight(s) to be hidden behind the spokes of a wheel such that the weight(s) are nearly not visible. The principle idea of hidden spokes placement is disclosed, for instance, in the publication of application DE 44 15 931 A1. As an example, FIG. 1 illustrates a design aluminum alloy wheel 100 having five equidistant spokes 120 with equal width. The optimal location under consideration of design requirements for a balancing weight 102 is depicted as behind a spoke 121 (the weight depicted as small box is marked by an arrow).
To automatize HSP, implementation of several functions in a wheel balancing apparatus is required. These functions comprise, for instance, measuring the unbalance of the wheel and calculation of the required optimal balancing weight(s). Further, determination of the spoke locations of the wheel and if necessary, calculation of the required split weights for hidden placement. These functions may be implemented in software where respective algorithms performing the required methods steps.
In particular, for HSP it is crucial that the wheel balancing apparatus, that is the control unit thereof, knows about the correct and exact positions and shape of the spokes of the vehicle wheel to be balanced. For that purpose, the wheel may be scanned in order to gather information about the spoke configuration of the wheel such as inter alia position of the spokes and width of the spokes.
U.S. Pat. No. 6,535,281 discloses a method and an apparatus for scanning a vehicle wheel, wherein a location on the wheel is sensed by means of a light beam emitted by a light source and is reflected to a position-sensitive receiver. The spacing of the sensed location relative to a reference location is measured from the directions of the emitted beam and the reflected beam. The light source and the position-sensitive receiver are synchronously pivoted about a common axis by means of a rotary drive including a stepping motor for successive measurement steps. A rotary angle sensor supplies signals proportional to the rotary position of the stepping motor to an evaluation system. By this method and apparatus it is possible to provide digitized scan data on the spoke configuration of the wheel to be balanced. That information is represented by the measured spacing of each sensed location relative to the respective reference location on the wheel.
However, to ensure efficient throughput of a wheel balancing apparatus the scan data should be reduced to a minimum as well as the elaboration thereof. Further, the elaboration of the scan data should be on the one hand as swift as possible and again be as reliable as possible.
However, modern wheels, in particular expensive wheels made of aluminum alloys, come in a great variety of spoke configurations. In other words, it is unlikely that all spokes have equal distances from each other. Even it is not a matter of fact that all spokes of a wheel have same width, as can be seen from FIG. 2a to 2g. 
In FIG. 2a, the spoke configuration of wheel 200a comprises a rim 210a with five equidistant pairs 230a of spokes 220a, wherein a pair 230a of spokes 220a has two equidistant spokes 220a with equal width. In FIG. 2b the wheel 200b comprises a rim 210b with oblique spokes 220b, wherein the spoke corresponds not to the shortest direct connection between the hub and the point on the rim where the base of the spoke is located. In FIG. 2c the spokes 220c of the wheel 200c form five equidistant pairs 230c, wherein the spokes 220c of a certain pair 230c have different dimensions alike different width. FIG. 2d shows a wheel 200d with bifurcate spokes 220d, wherein a certain spoke 220d runs form the hub 205d in direction of the rim 210d and before the spoke 220d reaches the rim 210d it branches in two spokes 221d, 222d. In FIG. 2e, the spoke configuration of wheel 200e comprises a rim 210e with five equidistant pairs 230e of spokes 220e, wherein a pair 230e of spokes 220e comprises two symmetrical spokes 220e, and wherein spaces 240e between the pairs of spokes 230e are formed like circles and spaces 241e within a pair of spokes 230e are formed as a slot. The wheel 200f in FIG. 2f comprises five groups 231f of spokes 220f, wherein two spokes of a group 231f are thin and one spoke is relatively broad. On the other hand, the spaces 240f of the wheel 200f are nearly equal and equidistant distributed. The wheel 200g in FIG. 2g is somewhat a hardening version of the wheel 100 of FIG. 1. The wheel 200g on the first glance looks easy to handle, however the small space 241g in the base of the spokes 220g are troublesome for HSP.
It is therefore an object of the present invention to provide a method and an apparatus for balancing wheels enabling automatized hidden spokes placement of balancing weights, whereby it is possible to handle as much as possible of the different kinds of spoke configurations as shortly discussed above.